Lost in dead wood? Environmental DNA metabarcoding from dead wood shows little signs of saproxylic beetles

eDNA metabarcoding of wood samples has become a standard method for sampling wood-inhabiting fungi and bacteria but sampling of saproxylic, i.e. dead-wood inhabiting, beetles still relies on time- consuming collection of beetle specimen. In a mesocosm experiment with manipulated species assemblages we test if beetle species can be identified by eDNA metabarcoding of wood. Dead wood samples were taken at exit holes of beetles, DNA extracted and analyzed by metabarcoding with standard arthropod primers (421 bp). However, we detected none of the target beetle species (in 34 samples), but one accidentally colonizing species. In addition we found 80 different OTUs including three species of arthropods. We suggest that in contrast to fungi and bacteria current eDNA metabarcoding approaches are not able to reliably detect saproxylic beetles from wood samples. Adapting such an approach for large scale analyses thus require a better knowledge of degradation processes affecting DNA quality and quantity in wood samples.